1. Field of the Invention
The present invention relates generally to a fluid filled type vibration damping device capable of providing vibration damping effect based on the flow action of a fluid sealed therein, and more particularly to a fluid filled type vibration damping device having a partition member disposed therein to form a plurality of fluid chambers, with the plurality of fluid chambers communicating with one another through an orifice passage.
2. Description of the Related Art
Fluid filled type vibration damping devices designed to produce vibration damping effect on the basis of resonance action or other fluid action of a fluid sealed in the interior are known as one type of vibration damping device such as a vibration damped coupling or vibration damped support designed for installation between components making up a vibration transmission system. In such a fluid filled type vibration damping device, as taught in JP-A-2003-139189 for example, a first metal mounting member is disposed on the side of a first opening of a second metal mounting member of tubular shape, the first mounting member and the second mounting member are elastically connected by a main rubber elastic body with one opening of the second mounting member being sealed off fluid-tightly, while the other opening of the second mounting member is sealed off fluid-tightly by a flexible film, thereby forming between the main rubber elastic body and the flexible film a fluid chamber in which a non-compressible fluid is sealed. A partition member supported by the second mounting member is disposed between the main rubber elastic body and the flexible film, thereby dividing the fluid chamber to form to either side of the partition member a pressure-receiving chamber whose wall is partially constituted by the main rubber elastic body and an equilibrium chamber whose wall is partially constituted by the flexible film, with the two chambers communicating with each other through an orifice passage.
For structural reasons, the partition member in a fluid filled type vibration damping device is sometimes composed of a plurality of superposed members. This is because complex shape or construction may be needed, for example, to form a long orifice passage, a plurality of orifice passages, or various other orifice passages, or to form an internal rubber film, auxiliary fluid chamber, air chamber or the like. To fasten such a partition member to the second mounting member, a plurality of members are superposed in the axial direction, fitted internally into the tubular wall portion of the second mounting member, and the tubular wall portion subjected to drawing or other diameter-constricting process, whereby the partition member composed of the plurality of members is fixedly fasten into the tubular wall portion. Mainly for the purpose of improving sealing of the orifice passage formed in the partition member, the outer circumferential face of each of the plurality of members is positioned in intimate contact against the inside peripheral face of the tubular wall portion, via a rubber layer formed on the inside peripheral face.
In a partition member of the kind described above, in order to facilitate handling, management, and the process of assembly with the second mounting member, it is preferable for the plurality of members to be fastened in the superposed state in advance, and subsequently fastened to the second mounting member. Conceivable ways of doing so are welding or bonding the plurality of members together, or fastening them press-fit together, in advance. However, fastening them inevitably requires special operations, materials, and equipment. As long as the plurality of members are ultimately fastened fitting into the second mounting member, it suffices for them to be fastened temporarily in the superposed state, so such fastening methods are not always appropriate.
Accordingly, there has been contemplated a mechanical locking mechanism, as means for temporarily fastening a plurality of members prior to fastening them fitting into the second mounting member. A specific example is that disclosed in JP-A-2004-144237, for example. JP-A-2004-144237 teaches a locking mechanism wherein at least one of two members to be fastened superposed to each other is a resin molding, with a locking projection being formed in one and a locking hole being formed in the other, and locked together by inserting the locking projection through the locking hole.
However, research carried out by the inventors has revealed the problem caused by differences in the assembly method of the second mounting member with the partition member. For instance, in cases where the partition member is fastened by means of drawing the tubular wall portion of the second mounting member for example, differences in the tubular wall portion drawing ratio or drawing diameter, or the contact surface area of the drawn portion, may possibly causes the problem that the locking projection which makes up part of the locking mechanism may be lost.
Specifically, when subjecting the tubular wall portion of the second mounting member to a diameter constricting process to fastening a partition member fitting therein, if the rubber layer covering the inside peripheral face of the tubular wall portion should become compressed in the axis-perpendicular direction between the tubular wall portion and the partition member, the rubber layer may undergo elastic deformation so as to contract in the axial direction. In association with contraction of the rubber layer, the plurality of members locked together in the axial direction by means of the locking mechanism are subjected to external force in the axial direction, acting in the direction moving them apart. It has been found that, the action of this external force possibly causes that the locking projection which has been formed of resin material as a temporarily fastening may break off owing to differences in assembly method as mentioned previously.
Break-off of the locking projection poses no problem with regard to fastening the plurality of members together, with the plurality of members fastened to the second mounting member. This is because the fastening force fastening the plurality of members together is provided by the members being fitted fastened on the basis of diameter constriction of the second mounting member. However, if the broken off locking projection should drop into the fluid chamber, there is a risk of it entering and clogging the orifice passage, or contacting the flexible film and damaging it.